Gray and Muddy Thinking about Global Warming

April 26th, 2006 by group

For years, perhaps decades, Gray has been ascribing all sorts of climate changes and hurricane cycles to fluctuations in the Thermohaline Circulation (THC), an overturning circulation in the Atlantic ocean associated with formation of deep water in the North Atlantic. None of the assertions are based on rigorous statistical associations, oceanographic observations or physically based simulations; it is all seat-of -the-pants stuff of a sort that was common in the early days of climate studies, but which is difficult to evaluate when viewed as a scientific hypothesis. The THC is undoubtedly important to climate, because it transports heat from one place to another. However it cannot do magical things. It cannot created energy out of thin air (or thick water), nor can it make energy mysteriously disappear. Thus, Gray’s statement that "The average THC circulation cools the ocean by about 3 W/m2" is a scientific absurdity. In the paper Gray makes many extravagant claims about how supposed changes in the THC accounted for various 20th century climate changes ("I judge our present global ocean circulation conditions to be similar to that of the period of the early 1940s when the globe had shown great warming since 1910, and there was concern as to whether this 1910-1940 global warming would continue. But beginning about 15 years following the onset of a strong THC circulation in 1926, in the early 1940s, the warming began to abate. A weak global cooling began from the mid-1940s to the mid-1970s.") but the reader would never guess that he in fact has no direct oceanographic evidence that the THC was doing anything of the sort. These are all subjective estimates based on Gray’s conception of the relation of Atlantic temperatures to the THC state. In fact, it is exceedingly difficult to directly monitor the THC, and reliable results have only recently been obtained. We have reported recently on the "Decrease in Atlantic Circulation". For years prior to the publication of evidence that the THC was slowing down, Gray was testifying in Congress and writing widely that hurricane increases were due to Atlantic warming arising from a speed-up of the THC (see our article for some typical quotes). Confronted with evidence that the THC was in fact behaving in the opposite way to what he had been assuming, Gray did a flip-flop and came up with a new story that yields the same conclusions. There’s no shame in a scientist changing his or her mind, or in seeking new theories in the face of new observations. However, if Gray’s old theory was really testable, where were the tests to show that it was wrong in the years he was touting it? How is one to put any confidence in the new theory? The fact is that neither of Gray’s story lines about the THC is sufficiently well formulated to allow any clear-cut test. Nonetheless, insofar as it can be understood at all, some aspects of Gray’s new story line about the THC are demonstrably wrong.